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<div class="titlepage"><div><div><h3 class="title">
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<a name="safe_numerics.tutorial.3"></a>Problem:Implicit conversions change data values</h3></div></div></div>
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<p>A simple assign or arithment expression will generally convert all
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the terms to the same type. Sometimes this can silently change values. For
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example, when a signed data variable contains a negative type, assigning
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to a unsigned type will be permitted by any C/C++ compiler but will be
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treated as large unsigned value. Most modern compilers will emit a compile
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time warning when this conversion is performed. The user may then decide
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to change some data types or apply a <code class="computeroutput">static_cast</code>. This is
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less than satisfactory for two reasons:</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem"><p>It may be unwield to change all the types to signed or
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unsigned.</p></li>
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<li class="listitem"><p>Litering one's program with <code class="computeroutput">static_cast</code><code class="computeroutput">
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</code>makes it more difficult to read.</p></li>
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<li class="listitem"><p>We may believe that our signed type will never contain a
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negative value. If we use a <code class="computeroutput">static_cast</code> to suppress the
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warning, we'll fail to detect a program error when it is commited.
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This is aways a risk with casts.</p></li>
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</ul></div>
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<p>This solution is the same as the above, Just replace instances of
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the <code class="computeroutput">int </code>with <code class="computeroutput">safe<int></code>.</p>
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<pre class="programlisting">void example2(){
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// problem: undetected overflow in data type
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try{
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int x = INT_MAX;
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// the following silently produces an incorrect result
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++x;
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//std::cout << x << " != " << -1;
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detected_msg(false);
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}
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catch(...){
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assert(false); // never arrive here
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}
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// solution: replace int with safe<int>
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try{
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using namespace boost::numeric;
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safe<int> x = INT_MAX;
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// throws exception when result is past maximum possible
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++x;
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assert(false); // never arrive here
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}
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catch(std::range_error & e){
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std::cout << e.what();
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detected_msg(true);
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}
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}
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</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2012 Robert Ramey<p><a href="???" target="_top">Subject to Boost Software License</a></p>
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